Method and apparatus for preparing microparticles using in-line solvent extraction

ABSTRACT

Apparatus and method for preparing microparticles using in-line solvent extraction. An emulsion is formed by combining two phases in a static mixer. The emulsion is combined with an extraction liquid in a blending static mixer. The outflow of the blending static mixer is combined with additional extraction liquid. The additional extraction liquid and the outflow of the blending static mixer can be combined in a vessel, or through the use of a static mixer manifold that includes a plurality of static mixers.

CROSS-REFERENCE TO RELATED APPLICATIONS

[0001] This application is related to application Ser. No. 09/438,659,filed Nov. 12, 1999, application Ser. No. 09/828,849, filed Apr. 10,2001, application Ser. No. 10/109,641, filed Apr. 1, 2002, applicationSer. No. 10/355,061, filed Jan. 31, 2003, and Ser. No. 10/713,039, filedNov. 17, 2003, the entirety of each of which is incorporated herein byreference.

BACKGROUND OF THE INVENTION

[0002] 1. Field of the Invention

[0003] The present invention relates to preparation of microparticles.More particularly, the present invention relates to a method and anapparatus for preparing microparticles using in-line solvent extraction.

[0004] 2. Related Art

[0005] A variety of methods is known by which compounds can beencapsulated in the form of microparticles. It is particularlyadvantageous to encapsulate a biologically active or pharmaceuticallyactive agent within a biocompatible, biodegradable wall forming material(e.g., a polymer) to provide sustained or delayed release of drugs orother active agents. In these methods, the material to be encapsulated(drugs or other active agents) is generally dissolved, dispersed, oremulsified, using stirrers, agitators, or other dynamic mixingtechniques, in a solvent containing the wall forming material. Solventis then removed from the microparticles and thereafter the microparticleproduct is obtained.

[0006] Development of a microencapsulation process suitable forcommercial scale production typically requires scaling up, by multiplefactors, a laboratory scale process and/or a pilot scale process. Thescaled-up process will almost always require larger piping and higherflow rates, particularly when the scale factor is very large or if it isdesired or necessary to keep process transfer times similar to thesmaller scale processes. Scale-up into new, larger equipment is oftenunpredictable and achieved in large measure through trial and error.However, the economic costs of large-scale trial and error experimentscan be prohibitive.

[0007] One approach to aiding the scale-up process is to use a staticmixer to form an emulsion, as disclosed in U.S. Pat. No. 5,654,008. Inthe method disclosed in U.S. Pat. No. 5,654,008, a first phase,comprising the active agent and the polymer, and a second phase arepumped through a static mixer into a quench liquid to formmicroparticles containing the active agent. The use of a static mixer toform the emulsion tends to make the scale-up more predictable andreliable than the scale-up of other dynamic-mixing processes for makingmicroparticles. However, numerous trials and experiments are stillrequired to completely and accurately scale-up, such as to commercialscale or by a factor of 20 or more, a process such as the one disclosedin U.S. Pat. No. 5,654,008.

[0008] Thus, there is a need in the art for an improved method andapparatus for preparing microparticles. There is a particular need inthe art for an improved process that can be more quickly, reliably, andaccurately scaled-up from a laboratory or pilot scale to a commercialscale. The present invention, the description of which is fully setforth below, solves the need in the art for such a method and apparatus.

SUMMARY OF THE INVENTION

[0009] The present invention relates to an apparatus and method forpreparing microparticles. In one aspect of the invention, a method ofpreparing microparticles is provided. The method comprises:

[0010] preparing a first phase, the first phase comprising an activeagent and a polymer;

[0011] preparing a second phase;

[0012] combining the first phase and the second phase in a first staticmixer to form an emulsion;

[0013] combining the emulsion and a first extraction liquid in a secondstatic mixer; and

[0014] combining an outflow of the second static mixer with a secondextraction liquid.

[0015] In one aspect of such a method, the outflow of the second staticmixer flows into a vessel containing the second extraction liquid. Inanother aspect, the outflow of the second static mixer flows into avessel, and the second extraction liquid is added to the vessel. Thesecond extraction liquid can be added to the vessel either while theoutflow of the second static mixer is flowing into the vessel, or afterthe outflow of the second static mixer has completed flowing into thevessel. In yet another aspect, the outflow of the second static mixerand the second extraction liquid can be combined in another staticmixer.

[0016] In a further aspect of the present invention, another method forpreparing microparticles is provided. The method comprises:

[0017] preparing a first phase, the first phase comprising an activeagent and a polymer;

[0018] preparing a second phase;

[0019] combining the first phase and the second phase in a first staticmixer to form an emulsion, the emulsion forming an outflow of the firststatic mixer;

[0020] combining the outflow of the first static mixer and a firstportion of a starting volume of an extraction liquid in a second staticmixer to form an outflow of the second static mixer;

[0021] dividing the outflow of the second static mixer to form at leasttwo flow streams;

[0022] flowing each of the at least two flow streams through a separatethird static mixer; and

[0023] combining the at least two flow streams with a second portion ofthe extraction liquid.

[0024] In one aspect of such a method, the at least two flow streamsflow into a vessel containing the second portion of the extractionliquid. In another aspect, the at least two flow streams and the secondportion of the extraction liquid are combined in a fourth static mixer.In yet another aspect, the at least two flow streams and the secondportion of the extraction liquid are combined in a fourth static mixer,and the combining step is repeated until the starting volume of theextraction liquid is depleted. The combining step may be repeated bycontinuing to combine the at least two flow streams and the extractionliquid in the fourth static mixer until the starting volume of theextraction liquid is depleted. Alternatively, the combining step may berepeated by combining the at least two flow streams and the extractionliquid in additional static mixers until the starting volume of theextraction liquid is depleted.

[0025] In a further aspect of the present invention, another method forpreparing microparticles is provided. The method comprises:

[0026] preparing a first phase, the first phase comprising an activeagent and a polymer;

[0027] preparing a second phase;

[0028] combining the first phase and the second phase in a first staticmixer to form an emulsion, the emulsion forming an outflow of the firststatic mixer;

[0029] combining the outflow of the first static mixer and a firstextraction liquid in a second static mixer to form an outflow of thesecond static mixer;

[0030] dividing the outflow of the second static mixer to form at leasttwo flow streams;

[0031] flowing each of the at least two flow streams through a separatethird static mixer; and

[0032] combining the at least two flow streams with a second extractionliquid.

[0033] In yet a further aspect of the present invention, amicroencapsulated active agent prepared by a method for preparingmicroparticles is provided. Such a method comprises:

[0034] preparing a first phase, the first phase comprising an activeagent and a polymer;

[0035] preparing a second phase;

[0036] combining the first phase and the second phase in a first staticmixer to form an emulsion;

[0037] combining the emulsion and a first extraction liquid in a secondstatic mixer; and

[0038] combining an outflow of the second static mixer with a secondextraction liquid.

[0039] In yet a further aspect of the present invention, amicroencapsulated active agent prepared by another method for preparingmicroparticles is provided. Such a method comprises:

[0040] preparing a first phase, the first phase comprising an activeagent and a polymer;

[0041] preparing a second phase;

[0042] combining the first phase and the second phase in a first staticmixer to form an emulsion, the emulsion forming an outflow of the firststatic mixer;

[0043] combining the outflow of the first static mixer and a firstportion of a starting volume of an extraction liquid in a second staticmixer to form an outflow of the second static mixer;

[0044] dividing the outflow of the second static mixer to form at leasttwo flow streams;

[0045] flowing each of the at least two flow streams through a separatethird static mixer; and

[0046] combining the at least two flow streams with a second portion ofthe extraction liquid.

[0047] In still a further aspect of the present invention, a system forpreparing microparticles is provided. The system includes a first andsecond pump, and a first static mixer in fluid communication with eachof the pumps. One of the pumps is configured to pump an organic phaseinto the first static mixer. One of the pumps is configured to pump acontinuous phase into the first static mixer. A manifold, comprising aplurality of static mixers, is in fluid communication with the firststatic mixer. A third pump, in fluid communication with the manifold, isconfigured to pump an extraction liquid. A second static mixer is influid communication with the manifold. An outflow of the first staticmixer and the extraction liquid flow through the manifold and thenthrough the second static mixer.

[0048] In another aspect, the system can include a third static mixer influid communication with the first static mixer and with the manifold.The outflow of the first static mixer and the extraction liquid arecombined in the third static mixer, prior to flowing through themanifold. The system may also include a vessel in fluid communicationwith the second static mixer so that an outflow of the second staticmixer flows into the vessel. A fourth pump may also be provided to pumpthe extraction liquid into the second static mixer.

FEATURES AND ADVANTAGES

[0049] It is a feature of the present invention that it can be used toprepare microparticles, including microparticles containing an activeagent.

[0050] It is another feature of the present invention that it allows forparallel flow streams for the in-line solvent extraction.

[0051] Yet another feature of the present invention is the ability toeasily use different extraction liquids during the process. The systemcan be configured to introduce such different extraction liquids at theappropriate time and processing point.

[0052] An advantage of the present invention is that it substantiallyreduces or eliminates the need for a separate quench or extraction tankthat contains a large volume of quench liquid, to remove solvent, and toform hardened microparticles.

[0053] The present invention advantageously enables the controlledextraction of the polymer solvent from a polymer/active agent droplet toform microparticles containing the active agent. The processadvantageously provides a level of solvent removal sufficient forcommercial products. The process also advantageously provides highloading efficiency, making it particularly useful for commercialproducts.

[0054] The process of the present invention advantageously provides amore consistent processing environment than conventional processes forforming microparticles. The in-line solvent extraction method of thepresent invention allows the emulsion droplets to all be exposed to thesame processing conditions. In contrast, in conventional processes usingan extraction tank or vessel, the processing conditions change over timeas the solvent is extracted from the emulsion droplets in the tank.

[0055] The consistent processing conditions and environment of thepresent invention advantageously result in a process that is lesstime-dependent or scale-dependent than alternative processes.

[0056] The present invention provides a method and apparatus that areparticularly advantageous for scale-up. The parallel path manifold ofthe present invention allows for capacity increases from an established(single path) system without full-scale trial and error experiments innew and different equipment. The total flow rate can be increased fromthe single path system based upon the number of flow streams in themanifold.

BRIEF DESCRIPTION OF THE FIGURES

[0057] The present invention is described with reference to theaccompanying drawings. In the drawings, like reference numbers indicateidentical or functionally similar elements.

[0058]FIG. 1 shows one embodiment of an equipment configuration forpreparing microparticles in accordance with the present invention;

[0059]FIG. 2 shows another embodiment of an equipment configuration forpreparing microparticles in accordance with the present invention;

[0060]FIG. 3 illustrates flow through a static mixer; and

[0061]FIG. 4 shows a static mixer suitable for use with the presentinvention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0062] Overview

[0063] The present invention provides an improved method and apparatusfor preparing microparticles. The apparatus and methods of the presentinvention use in-line solvent extraction to provide a process that ismore scalable, with less overall processing time, than conventionalmethods.

[0064] The methods of the present invention use a static mixer tocombine a first phase, comprising an active agent and a polymer, with asecond phase to form an emulsion. A process for forming an emulsionusing a static mixer is described, for example, in U.S. Pat. No.5,654,008, the entirety of which is incorporated herein by reference.The phase comprising the active agent and the polymer may be referred toherein as the “organic phase”. The other phase may be referred to hereinas the “continuous phase”.

[0065] The outflow of the static mixer in which the emulsion is formedis combined with an extraction liquid in another static mixer that maybe referred to herein as a “blending static mixer”. In one embodiment,the outflow of the blending static mixer flows into a vessel where it iscombined with additional extraction liquid that may be the same ordifferent from the extraction liquid added to the blending static mixer.In another embodiment, the outflow of the blending static mixer isdivided into a plurality of flow streams that flow through a manifoldcontaining a plurality of static mixers. The plurality of flow streamsare recombined downstream, and combined with additional extractionliquid. In a particularly preferred embodiment, the recombined flowstreams and the additional extraction liquid are combined in anotherstatic mixer, and this combining step is repeated until the startingvolume of the extraction liquid is depleted. Such an embodimenteliminates the need for an extraction tank for extracting solvent.

[0066] In the present invention a blending static mixer is used tocombine the emulsion and the extraction liquid to form a combined flowstream. In one embodiment, the combined flow stream is divided into aplurality of flow streams for flow through the manifold. The use of theblending static mixer prior to the manifold is particularly advantageousbecause the emulsion and the extraction liquid may not be immediatelymiscible or homogeneous, making the division of the combined flow streamproblematic. For multiphase streams such as the combined emulsion andextraction liquid, the use of the manifold without the blending staticmixer could result in different compositions in each static mixer in themanifold. Because the combined emulsion and extraction liquid is nothomogeneous, it would not divide evenly in conventional piping.

[0067] The manifold configuration of the present invention isparticularly advantageous for scale-up. The parallel path manifold ofthe smaller diameter static mixers allows for capacity increases from anestablished (single path) system without full-scale trial and errorexperiments in new and different equipment. The total flow rate can beincreased from the single path system based upon the number of flowstreams in the manifold.

[0068] To ensure clarity of the description that follows, the followingdefinitions are provided. By “microparticles” or “microspheres” is meantsolid particles that contain an active agent or other substancedispersed or dissolved within a polymer that serves as a matrix orbinder of the particle. The polymer is preferably biodegradable andbiocompatible. By “biodegradable” is meant a material that shoulddegrade by bodily processes to products readily disposable by the bodyand should not accumulate in the body. The products of thebiodegradation should also be biocompatible with the body. By“biocompatible” is meant not toxic to the body, is pharmaceuticallyacceptable, is not carcinogenic, and does not significantly induceinflammation in body tissues. As used herein, “body” preferably refersto the human body, but it should be understood that body can also referto a non-human animal body. By “weight %” or “% by weight” is meantparts by weight per total weight of microparticle. For example, 10 wt. %active agent would mean 10 parts active agent by weight and 90 partspolymer by weight. Unless otherwise indicated to the contrary,percentages (%) reported herein are by weight. By “controlled releasemicroparticle” or “sustained release microparticle” is meant amicroparticle from which an active agent or other type of substance isreleased as a function of time. By “mass median diameter” is meant thediameter at which half of the distribution (volume percent) has a largerdiameter and half has a smaller diameter.

METHOD AND EXAMPLES

[0069] The following examples are provided to explain the invention, andto describe the materials and methods used in carrying out theinvention. The examples are not intended to limit the invention in anymanner.

Example 1 Preparation of Risperidone Microparticles

[0070] Microparticles comprising risperidone were prepared at theone-kilogram scale. The 1 Kg process (400 grams of active agent and 600grams of polymer) provides a theoretical drug loading of themicroparticles of 40% (400 grams/1000 grams×100%).

[0071] A 16.7% polymer solution was prepared by dissolving 600 grams ofMEDISORB® 7525 DL polymer (Alkermes, Inc., Blue Ash, Ohio) in ethylacetate. A 24% drug solution was prepared by dissolving 400 grams ofrisperidone base (Janssen Pharmaceutica, Beerse, Belgium) in benzylalcohol. The organic phase was prepared by mixing the drug solution intothe polymer solution. The continuous or aqueous phase was 30 Kg of a 1%polyvinyl alcohol (PVA) solution containing 6.5% ethyl acetate.

[0072] The emulsification step used two positive displacement pumps thatfed the individual phases (one pump for the organic phase and one pumpfor the aqueous phase) to a connecting union where they were combined. A5:1 aqueous phase to organic phase ratio was maintained throughout theemulsification step, at an average total flow rate of 3.2 Kg/min.Immediately following the connecting union in the processing stream wasa ½ inch diameter in-line mixer, four feet in length. The exitingemulsion (outflow of the static mixer) was then mixed with an amount ofa first extraction solution that was pumped via a peristaltic pump at anaverage flow rate of 9 Kg/min. The total volume of the first extractionsolution that was transferred was 100 Kg.

[0073] The combined stream (diluted mixture of emulsion and firstextraction solution) was then passed through a 1-inch diameter in-linestatic mixer (blending static mixer) 16 inches in length. The mixturewas then passed through approximately 56 inches of transfer piping toreach 144 Kg of a second extraction solution contained in a stirredholding vessel. The mixture was stirred for 4 to 6 hours in the holdingvessel. Samples were periodically taken to determine the levels ofresidual solvent(s), and to determine loading efficiency. Loadingefficiency is the ratio, expressed as a percentage, of the actual drugloading to the theoretical drug loading.

[0074] Two experiments were done using the one-kilogram risperidonepartial in-line extraction method described above. In Experiment One,the first and second extraction solutions both contained 2.5% ethylacetate. In Experiment Two, the first extraction solution contained 2.5%ethyl acetate, and the second extraction solution was pure water.

[0075] The residual solvent levels and loading efficiencies obtainedfrom the two experiments were compared to a control. The control was theaverage of four one-kilogram batches of risperidone microparticlesprepared in the following manner. For each of the four control batches,the same steps were used to prepare the organic and aqueous phases as inthe partial in-line extraction method described above, and the sameemulsification step was also used. However, for each of the four controlbatches, the emulsion exiting the first static mixer was thentransferred into a holding vessel that contained an aqueous extractionsolution containing 2.5% ethyl acetate.

[0076] A comparison of the results obtained in Experiments One and Twowith the risperidone control is shown below in Table 1. Table 1 showsthe level of residual solvent for both ethyl acetate (Et/Ac) and benzylalcohol (BA) for Experiments One and Two and the control. As shown inTable 1, the levels of residual solvent for Experiment One (3.6/5.1%)were comparable to the levels of residual solvent for the risperidonecontrol (3.0/5.0%). In Experiment Two, the residual BA solvent level(9.5%) was significantly higher than the risperidone control BA solventlevel (5.0%). The rate of extraction of each solvent is affected by theconcentration of ethylacetate in the extraction solution, for example asdescribed in U.S. Pat. No. 5,650,173, the entirety of which isincorporated therein by reference. The results obtained in ExperimentTwo for the residual benzyl alcohol level of 9.5% were comparable,however, to another risperidone control processed without an initialethyl acetate component in the extraction solution, resulting in aresidual benzyl alcohol level in the microparticles of 9.3%. The lowerresidual solvent level of ethyl acetate in Experiment Two (0.9%) is alsolikely the result of the lack of ethyl acetate in the second extractionsolution. TABLE 1 Risperidone Process Partial In-Line ExtractionExperiment # Risperidone Control One Two 1 kg Average Residual Solvents3.6/5.1% 0.9/9.5% 3.0/5.0% (EtAc/BA) Loading Efficiency 92.2% 88.0%93.2%

[0077] As shown in Table 1, the loading efficiency of Experiment One(92.2%) was comparable to that of the risperidone control (93.2%). The93.2% loading efficiency for the risperidone control is the loadingefficiency of the final microparticle product after the residual solventlevels of ethyl acetate and benzyl alcohol are reduced to 1-2%. Loadingefficiency for the same product containing 5-9% residual solvent levelsof ethyl acetate and benzyl alcohol are expected to be lower due to massbalance. This is consistent with the results obtained in Experiment Two,with a lower loading efficiency of 88.0%.

EXAMPLE 2 Preparation of Bupivacaine Microparticles

[0078] Microparticles comprising bupivacaine were prepared at thetwenty-gram scale. The 20 gram process (4 grams of active agent and 16grams of polymer) provides a theoretical drug loading of themicroparticles of 20% (4 grams/20 grams×100%).

[0079] Sixteen grams of MEDISORB® 7525 DL polymer (Alkermes, Inc., BlueAsh, Ohio) and four grams of bupivacaine base were dissolved in 230grams of ethyl acetate to make the organic phase. The aqueous phaseconsisted of a 1% PVA solution containing a saturating amount of polymersolvent (ethyl acetate), with a pH of 8.5 and a trizma bufferconcentration of 0.05 molar. The extraction solution was a 0.05 molartrizma buffered aqueous solution at a pH of 8.5

[0080] The emulsification step used two positive displacement pumps thatfed the individual phases (one pump for the organic phase and one pumpfor the aqueous phase) to a connecting union where they were combined.The organic phase pump operated at 75 ml/min, and the aqueous phase pumpoperated at 150 ml/mm. A 3:1 aqueous phase to organic phase ratio wasmaintained throughout the emulsification step. Immediately following theconnecting union was a ¼ inch diameter in-line static mixer, 17 and ½inches in length. The exiting emulsion (outflow of the static mixer) wasthen mixed with an amount of the extraction solution that was pumped viaa positive displacement pump at an extraction solution to emulsion ratioof 1:1. This extraction solution pump operated at 225 ml/min.

[0081] The combined stream (diluted mixture of emulsion and firstextraction solution) was then passed through a ⅜-inch diameter in-linestatic mixer (blending static mixer) 4 and ¾ inches in length. Eventhough extraction of solvents is occurring in the blending static mixer,at this point in the process stream, the microdroplets of the emulsionhave not fully hardened, and further processing is needed to ensuredesired particle size. The outflow of the blending static mixer wasdivided into two flow streams, each then passing through a separateindividual ¼ inch diameter in-line static mixer 6 inches in length. Thetwo flow streams create less shear in each flow stream, tending tocreate microparticles of larger size. With only one large flow stream,there may be sufficient shear to result in smaller size microparticles.The two flow streams were then recombined, and added to a flow stream ofthe extraction solution that was pumped via a positive displacement pumpoperating at 450 ml/min. The resulting flow stream was passed through a½ inch diameter in-line static mixer that was 12 inches in length, andthen collected in an initially empty holding vessel. The two extractionsolution pumps were started at the same time as the aqueous phase pump,and operated continuously.

[0082] After the organic phase had been exhausted, the contents in theholding vessel were gently mixed via an overhead agitator and theremaining extraction solution was transferred to the holding vessel. Themixture was agitated for an hour. The microparticles were recovered on a25 micron screen, dried in a hood overnight, and analyzed for residualsolvent level and loading efficiency.

[0083] The residual solvent level and loading efficiency obtained fromthe 20 gram bupivacaine process were compared to a 20 gram bupivacainecontrol. The 20 gram bupivacaine control was made using the sameaqueous, organic, and extraction solution, and concentrations thereof,as in the bupivacaine in-line extraction method described above. Theemulsification step was the same as described above, except for the useof a ¼ inch diameter, 16 inch long in-line static mixer to create theemulsion. The emulsion exiting this static mixer was then transferredinto the total volume of the extraction solution that was contained inthe stirred holding vessel.

[0084] A comparison of the results obtained using the bupivacainein-line extraction method (“bupivacaine process”) with the bupivacainecontrol is shown below in Table 2. As shown in Table 2, the level ofresidual solvent for the bupivacaine process is identical to the levelof residual solvent for the bupivacaine control (4.2%). The loadingefficiency for the bupivacaine process (75%) is comparable to theloading efficiency for the bupivacaine control (88.5%). TABLE 2Bupivacaine Process In-Line Extraction Bupivacaine Control Batch Size 20gram 20 gram Residual Solvent (EtAc) 4.2%   4.2% Loading Efficiency 75%88.5%

[0085] Examples 1 and 2 demonstrate that the process of the presentinvention enables the controlled extraction of the polymer solvent froma polymer/active agent droplet to form microparticles containing theactive agent. Each of the emulsion droplets are exposed to substantiallythe same processing conditions throughout the process. The initialhardening of the emulsion droplets is not time or scale-dependent, as inconventional encapsulation processes. The process of the presentinvention provides a level of solvent removal sufficient for commercialproducts. The process also provides high loading efficiency, making itparticularly useful for commercial products.

EXAMPLE 3 Methods for Preparing Microparticles

[0086] As exemplified by the examples discussed above, methods forpreparing microparticles in accordance with the present invention willnow be described in more detail. Exemplary apparatus suitable forcarrying out such methods will be described below. In one embodiment ofthe present invention, a first phase, comprising an active agent and apolymer, is prepared. In one embodiment of the present invention, thefirst phase is prepared by dissolving the active agent in a firstsolvent to form an active agent solution. The polymer is dissolved in asecond solvent to form a polymer solution. The active agent solution andthe polymer solution are blended to form the first phase. In aparticularly preferred embodiment, the active agent is selected from thegroup consisting of risperidone, 9-hydroxyrisperidone, andpharmaceutically acceptable salts thereof. In such an embodiment, apreferred first solvent is benzyl alcohol, and a preferred secondsolvent is ethyl acetate.

[0087] In another embodiment of the present invention, the first phaseis prepared by dissolving the active agent and the polymer in a solventto form a solution. In a particularly preferred embodiment, the activeagent is bupivacaine, and the solvent is ethyl acetate. It should beunderstood that the present invention is not limited to any particularmethod or process by which the first phase is prepared, and othersuitable processes would be readily apparent to one skilled in the art.

[0088] A second phase is prepared, and combined with the first phase ina first static mixer to form an emulsion. In a preferred embodiment, thetwo phases are pumped into the static mixer, with the second phase beingpumped at a flow rate greater than the flow rate of the first phase. Inone preferred embodiment, the ratio of the flow rate of the second phaseto the flow rate of the first phase is approximately 2:1. Exemplaryratios of the volume of the second phase to the volume of the firstphase are approximately 5:1 and approximately 3:1. However, it should beunderstood by one skilled in the art that the present invention is notlimited to such a flow rate ratio or volume ratios, and otherappropriate flow rate ratios and volume ratios would be readily apparentto one skilled in the art.

[0089] The emulsion is combined with a first extraction liquid in asecond static mixer. In a preferred embodiment, the first extractionliquid is pumped at a first rate into the emulsion flowing out of thefirst static mixer to form a first combined stream. The first combinedstream is then allowed to flow through the second static mixer. Thevolume ratio of the emulsion to the first extraction liquid can beapproximately 1:1, although it should be readily apparent to one skilledin the art that other volume ratios can be used. In one embodiment, thesecond static mixer comprises a plurality of individual static mixersconfigured to provide a plurality of parallel flow streams. In aparticularly preferred embodiment, the plurality of individual staticmixers is two. However, it should be understood by one skilled in theart that the present invention is not limited to the use of twoindividual static mixers in such a configuration, and other appropriatenumbers of individual static mixers would be readily apparent to oneskilled in the art.

[0090] The outflow of the second static mixer is combined with a secondextraction liquid. The second extraction liquid can be the same as, ordifferent from, the first extraction liquid. The second extractionliquid can be the same as, or different from, the second phase.Similarly, the first extraction liquid can be the same as, or differentfrom, the second phase.

[0091] In one embodiment of the present invention, the outflow of thesecond static mixer flows into a vessel that contains the secondextraction liquid. In an alternate embodiment, the outflow of the secondstatic mixer flows into the vessel, and the second extraction liquid isadded to the vessel. The second extraction liquid can be added to thevessel either while the outflow of the second static mixer is flowinginto the vessel, or after the outflow of the second static mixer hascompleted flowing into the vessel.

[0092] In a further embodiment of the present invention, the outflow ofthe second static mixer is combined with the second extraction liquid ina third static mixer. Preferably, the second extraction liquid is pumpedat a second rate into the outflow of the second static mixer to form asecond combined stream, and the second combined stream is allowed toflow through the third static mixer. In one embodiment, the second rateof pumping the second extraction liquid is greater than the first rateof pumping the first extraction liquid. However, the present inventionis not limited to such pumping rates, and suitable pumping rates wouldbe readily apparent to one skilled in the art.

[0093] The third static mixer can be an individual static mixer, aplurality of individual static mixers arranged in series, or a pluralityof individual static mixers configured to provide a plurality ofparallel flow streams. The outflow of the third static mixer flows intoa vessel. The vessel can be empty prior to allowing the outflow of thethird static mixer to flow therein. Alternatively, the vessel cancontain an extraction liquid or other type of quench solution prior toallowing the outflow of the third static mixer to flow therein.

[0094] An alternate method for preparing microparticles in accordancewith the present invention will now be described. A first phase,comprising an active agent and a polymer, is prepared. A second phase isprepared, and combined with the first phase in a first static mixer toform an emulsion, the emulsion forming an outflow of the first staticmixer. Suitable methods and processes for preparing the first and secondphases, and for combining in the first static mixer, have been describedabove and will not be repeated here for brevity.

[0095] The outflow of the first static mixer is combined with a firstportion of a starting volume of an extraction liquid in a second staticmixer to form an outflow of the second static mixer. The extractionliquid can be the same as, or different from, the second phase. Thesecond static mixer can be an individual static mixer, a plurality ofindividual static mixers arranged in series, or a plurality ofindividual static mixers configured to provide a plurality of parallelflow streams.

[0096] The outflow of the second static mixer is divided to form atleast two flow streams. Each of the at least two flow streams flowsthrough a separate third static mixer. The separate third static mixercan be an individual static mixer, one of a plurality of individualstatic mixers arranged in series, or one of a plurality of individualstatic mixers configured to provide a plurality of parallel flowstreams.

[0097] The at least two flow streams are combined with a second portionof the extraction liquid. In an alternate embodiment of the presentinvention, the at least two flow streams are combined with anotherextraction liquid different from the first portion of the extractionliquid. This other extraction liquid can be the same as, or differentfrom, the second phase.

[0098] In one embodiment of the present invention, the at least two flowstreams are combined with the second portion of the extraction liquid byallowing the at least two flow streams to flow into a vessel containingthe second portion of the extraction liquid. In an alternate embodiment,the at least two flow streams are combined with the second portion ofthe extraction liquid in a fourth static mixer. The outflow of thefourth static mixer can then flow into a vessel. In a particularlypreferred embodiment, the at least two flow streams are combined withthe second portion of the extraction liquid in a fourth static mixer,and this combining step is continued until the starting volume of theextraction liquid is depleted.

[0099] Microparticles of the Present Invention

[0100] The microparticles prepared by the process of the presentinvention preferably comprise a polymeric binder, but it should beunderstood by one skilled in the art that the present invention is notlimited to preparation of microparticles comprising a polymeric binder.Suitable polymeric binder materials include poly(glycolic acid),poly-d,1-lactic acid, poly-1-lactic acid, copolymers of the foregoing,poly(aliphatic carboxylic acids), copolyoxalates, polycaprolactone,polydioxanone, poly(ortho carbonates), poly(acetals), poly(lacticacid-caprolactone), polyorthoesters, poly(glycolic acid-caprolactone),polyanhydrides, polyphosphazines, albumin, casein, and waxes. Poly(d,1-lactic-co-glycolic acid) is commercially available from Alkermes,Inc. (Blue Ash, Ohio). A suitable product commercially available fromAlkermes, Inc. is a 50:50 poly(d,1-lactic-co-glycolic acid) known asMEDISORB® 5050 DL. This product has a mole percent composition of 50%lactide and 50% glycolide. Other suitable commercially availableproducts are MEDISORB® 6535 DL, 7525 DL, 8515 DL and poly(d,l-lacticacid) (100 DL). Poly(lactide-co-glycolides) are also commerciallyavailable from Boehringer Ingelheim (Germany) under its Resomer® mark,e.g., PLGA 50:50 (Resomer® RG 502), PLGA 75:25 (Resomer® RG 752) andd,1-PLA (Resomer® RG 206), and from Birmingham Polymers (Birmingham,Ala.). These copolymers are available in a wide range of molecularweights and ratios of lactic acid to glycolic acid.

[0101] One type of microparticle suitable for preparation by the presentinvention is a sustained-release microparticle that is biodegradable.However, it should be understood by one skilled in the art that thepresent invention is not limited to biodegradable or other types ofsustained-release microparticles. As would be apparent to one skilled inthe art, the molecular weight of the polymeric binder material forbiodegradable microparticles is of some importance. The molecular weightshould be high enough to permit the formation of satisfactory polymercoatings, i.e., the polymer should be a good film former. Usually, asatisfactory molecular weight is in the range of 5,000 to 500,000daltons, preferably about 150,000 daltons. However, since the propertiesof the film are also partially dependent on the particular polymericbinder material being used, it is very difficult to specify anappropriate molecular weight range for all polymers. The molecularweight of the polymer is also important from the point of view of itsinfluence upon the biodegradation rate of the polymer. For a diffusionalmechanism of drug release, the polymer should remain intact until all ofthe drug is released from the microparticles and then degrade. The drugcan also be released from the microparticles as the polymeric binderbioerodes. By an appropriate selection of polymeric materials amicroparticle formulation can be made in which the resultingmicroparticles exhibit both diffusional release and biodegradationrelease properties. This is useful in according multiphasic releasepatterns.

[0102] The microparticles prepared in accordance with the presentinvention may include an active agent or other type of substance that isreleased from the microparticles into the host. Such active agents caninclude 1,2-benzazoles, more particularly, 3-piperidinyl-substituted1,2-benzisoxazoles and 1,2-benzisothiazoles. The most preferred activeagents of this kind are3-[2-[4-(6-fluoro-1,2-benzisoxazol-3-yl)-1-piperidinyl]ethyl]-6,7,8,9-tetrahydro-2-methyl-4H--pyrido[1,2-a]pyrimidin-4-one(“risperidone”) and 3-[2-[4-(6-fluro-1,2-benzisoxazol-3-yl)-1-piperidinyl]ethyl]-6,7,8,9-tetrahydro-9-hydroxy-2-methyl-4H-pyrido[1,2-a]pyrimidin-4-one(“9-hydroxyrisperidone”) and the pharmaceutically acceptable saltsthereof. Risperidone (which term, as used herein, is intended to includeits pharmaceutically acceptable salts) is most preferred. Risperidonecan be prepared in accordance with the teachings of U.S. Pat. No.4,804,663, the entirety of which is incorporated herein by reference.9-hydroxyrisperidone can be prepared in accordance with the teachings ofU.S. Pat. No. 5,158,952, the entirety of which is incorporated herein byreference.

[0103] Other biologically active agents include non-steroidalantifertility agents; parasympathomimetic agents; psychotherapeuticagents; major tranquilizers such as chlorpromazine HC1, clozapine,mesoridazine, metiapine, reserpine, thioridazine and the like; minortranquilizers such as chlordiazepoxide, diazepam meprobamate, temazepamand the like; rhinological decongestants; sedative-hypnotics such ascodeine, phenobarbital, sodium pentobarbital, sodium secobarbital andthe like; steroids such as testosterone and tesosterone propionate;.sulfonamides; sympathomimetic agents; vaccines; vitamins and nutrientssuch as the essential amino acids; essential fats and the like;antimalarials such 4-aminoquinolines, 8-aminoquinolines, pyrimethamineand the like, anti-migraine agents such as mazindol, phentermine and thelike; anti-Parkinson agents such as L-dopa; anti-spasmodics such asatropine, methscopolamine bromide and the like; antispasmodics andanticholinergic-agents such as bile therapy, digestants, enzymes and thelike; antitussives such as dextromethorphan, noscapine and the like;bronchodilators; cardiovascular agents such as anti-hypertensivecompounds, Rauwolfia alkaloids, coronary vasodilators, nitroglycerin,organic nitrates, pentaerythritotetranitrate and the like; electrolytereplacements such as potassium chloride; ergotalkaloids such asergotamine with and without caffeine, hydrogenated ergot alkaloids,dihydroergocristine methanesulfate, dihydroergocomine methanesulfonate,dihydroergokroyptine methanesulfate and combinations thereof; alkaloidssuch as atropine sulfate, Belladonna, hyoscine hydrobromide and thelike; analgetics, narcotics such as codeine, dihydrocodienone,meperidine, morphine and the like; non-narcotics such as salicylates,aspirin, acetaminophen, d-propoxyphene and the like; antibiotics such assalicylates, aspirin, acetaminophen, d-propoxyphene and the like;antibiotics such as the cephalosporins, chloranphenical, gentamicin,Kanamycin A, Kanamycin B, the penicillins, ampicillin, streptomycin A,antimycin A, chloropamtheniol, metromidazole, oxytetracycline penicillinG, the tetracylines, and the like, anti-cancer agents; anti-convulsantssuch as mephenytoin, phenobarbital, trimethadione; anti-emetics such asthiethylperazine; antihistamines such as chlorophinazine,dimenhydrinate, diphenhydramine, perphenazine, tripelennamine and thelike; anti-inflammatory agents such as hormonal agents, hydrocortisone,prednisolone, prednisone, non-hormonal agents, allopurinol, aspirin,indomethacin, phenylbutazone and the like; prostaglandins; cytotoxicdrugs such as thiotepa; chlorambucil, cyclophosphamide, melphalan,nitrogen mustard, methotrexate and the like; antigens of suchmicroorganisms as Neisseria gonorrhea, Mycobacterium tuberculosis,Herpes virus (homonis, types 1 and 2), Candida albicans, Candidatropicalis, Trichomonas vaginalis, Haemophilus vaginalis, Group BStreptococcus ecoli, Mycoplasma hominis, Haemophilus ducreyi, Granulomainguinale, Lymphopathia venereum, Treponema pallidum, Brucella abortus,Brucella melitensis, Brucella suis, Brucella canis, Campylobacter fetus,Campylobacter fetus intestinalis, Leptospira pomona, Listeriamonocytogenes, Brucella ovis, Equine herpes virus 1, Equine arteritisvirus, IBR-IBP virus, BVD-MB virus, Chlamydia psittaci, Trichomonasfoetus, Toxoplasma gondii, Escherichia coli, Actinobacillus equuli,Salmonella abortus ovis, Salmonella abortus equi, Pseudomonasaeruginosa, Corynebacterium equi, Corynebacterium pyogenes,Actinobacillus seminis, Mycoplasma bovigenitalium, Aspergillusfumigatus, Absidia ramosa, Trypanosoma equiperdum, Babesia caballi,Clostridium tetani, and the like; antibodies that counteract the abovemicroorganisms; and enzymes such as ribonuclease, neuramidinase,trypsin, glycogen phosphorylase, sperm lactic dehydrogenase, spermhyaluronidase, adenosinetriphosphatase, alkaline phosphatase, alkalinephosphatase esterase, amino peptidase, trypsin, chymotrypsin, amylase,muramidase, acrosomal proteinase, diesterase, glutamic aciddehydrogenase, succinic acid dehydrogenase, beta-glycophosphatase,lipase, ATP-ase alpha-peptate gamma-glutamylotranspeptidase,sterol-3-beta-ol-dehydrogenase, and DPN-di-aprorasse.

[0104] Other suitable active agents include estrogens such as diethylstilbestrol, 17-beta-estradiol, estrone, ethinyl estradiol, mestranol,and the like; progestins such as norethindrone, norgestryl, ethynodioldiacetate, lynestrenol, medroxyprogesterone acetate, dimesthisterone,megestrol acetate, chlormadinone acetate, norgestimate, norethisterone,ethisterone, melengestrol, norethynodrel and the like; and thespermicidal compounds such as nonylphenoxypolyoxyethylene. glycol,benzethonium chloride, chlorindanol and the like.

[0105] Still other suitable active agents include antiflngals,antivirals, anticoagulants, anticonvulsants, antidepressants,antihistamines, hormones, vitamins and minerals, cardiovascular agents,peptides and proteins, nucleic acids, immunological agents, antigens ofsuch bacterial organisms as Streptococcus pneumoniae, Haemophilusinfluenzae, Staphylococcus aureus, Streptococcus pyogenes,Corynebacterium diphtheriae, Bacillus anthracis, Clostridium tetani,Clostridium botulinum, Clostridium perfringens, Streptococcus mutans,Salmonella typhi, Haemophilus parainfluenzae, Bordetella pertussis,Francisella tularensis, Yersinia pestis, Vibrio cholerae, Legionellapneumophila, Mycobacterium leprae, Leptospira interrogans, Borreliaburgdorferi, Campylobacter jejuni, antigens of such viruses as smallpox,influenza A and B, respiratory syncytial, parainfluenza, measles, HIV,varicella-zoster, herpes simplex 1 and 2, cytomegalovirus, Epstein-Barr,rotavirus, rhinovirus, adenovirus, papillomavirus, poliovirus, mumps,rabies, rubella, coxsackieviruses, equine encephalitis, Japaneseencephalitis, yellow fever, Rift Valley fever, lymphocyticchoriomeningitis, hepatitis B, antigens of such fungal protozoan, andparasitic organisms such as Cryptococcus neoformans, Histoplasmacapsulatum, Candida albicans, Candida tropicalis, Nocardia asteroides,Rickettsia ricketsii, Rickettsia typhi, Mycoplasma pneumoniae, Chlamydiapsittaci, Chlamydia trachomatis, Plasmodium falciparum, Trypanosomabrucei, Entamoeba histolytica, Toxoplasma gondii, Trichomonas vaginalis,Schistosoma mansoni. These antigens may be in the form of whole killedorganisms, peptides, proteins, glycoproteins, carbohydrates, orcombinations thereof.

[0106] Still other macromolecular bioactive agents that may be chosenfor incorporation include, but are not limited to, blood clottingfactors, hemopoietic factors, cytokines, interleukins, colonystimulating factors, growth factors, and analogs and fragments thereof.

[0107] The microparticles can be mixed by size or by type. However, itshould be understood that the present invention is not limited to theuse of biodegradable or other types of microparticles that contain anactive agent. In one embodiment, the microparticles are mixed in amanner that provides for the delivery of active agent to the patient ina multiphasic manner and/or in a manner that provides different activeagents to the patient at different times, or a mixture of active agentsat the same time. For example, secondary antibiotics, vaccines, or anydesired active agent, either in microparticle form or in conventional,unencapsulated form can be blended with a primary active agent andprovided to the patient.

[0108] Apparatus

[0109] Turning now to FIG. 1, one embodiment of the apparatus of thepresent invention is shown (system 100). A first phase 110 and a secondphase 120 are pumped via a pump 112 and a pump 122, respectively, into afirst static mixer 130 to form an emulsion. The first phase preferablycomprises an active agent and a polymer, and is preferably in the formof a solution. The second phase is preferably an aqueous solution thatfunctions as the continuous phase of the emulsion.

[0110] A static or motionless mixer consists of a conduit or tube inwhich is received a number of static mixing elements. Static mixersprovide uniform mixing in a relatively short length of conduit, and in arelatively short period of time. With static mixers, the fluid movesthrough the mixer, rather than some part of the mixer, such as a blade,moving through the fluid. Flow through one type of static mixer isillustrated in FIG. 3. A pump (not shown) introduces a stream of one ormore fluids into a static mixer 10, as shown generally at 1. The streamis split and forced to opposite outside walls, as shown generally at 2.A vortex is created axial to the centerline of static mixer 10, as showngenerally at 3. The vortex is sheared and the process recurs, but withthe opposite rotation, as shown generally at 4. Theclockwise/counterclockwise motion ensures a homogeneous product.

[0111] One example of a static mixer is shown in FIG. 4. Static mixer 10includes a number of stationary or static mixing elements 14 arranged ina series within a conduit or pipe 12. The number of static mixingelements can range from 4 to 32 or more. Conduit 12 is circular incross-section and open at opposite ends 18 and 20 for introducing andwithdrawing fluids. Mixing element 14 comprises segments 42. Eachsegment 42 consists of a plurality of generally flat plates or vanes 44.The two substantially identical segments 42 are preferably axiallystaggered with respect to each other. A static mixer as shown in FIG. 4is more fully described in U.S. Pat. No. 4,511,258, the entirety ofwhich is incorporated herein by reference.

[0112] The emulsion is combined with a first extraction liquid 150,pumped via a pump 152, in a second static mixer 140. Static mixer 140functions as a blending static mixer to blend the emulsion and the firstextraction liquid. The outflow of second static mixer 140 flows into avessel 160. In one embodiment of the present invention, vessel 160contains a second extraction liquid. The second extraction liquid can bethe same as, or different from, the first extraction liquid. In furtherembodiments of the invention, second phase 120 can be used as the firstextraction liquid and/or the second extraction liquid.

[0113] In another embodiment of the present invention, the outflow ofsecond static mixer 140 flows into vessel 160, and the second extractionliquid is added to vessel 160. The second extraction liquid can be addedto vessel 160 either while the outflow of second static mixer 140 isflowing into vessel 160, or after the outflow of second static mixer 140has completed flowing into vessel 160.

[0114] Static mixer 140 is shown in FIG. 1 as an individual staticmixer. Alternatively, static mixer 140 could be configured as a manifoldthat includes a plurality of individual static mixers arranged inparallel to provide a plurality of parallel flow streams, as shown, forexample, by manifold 240 illustrated in FIG. 2. Alternatively, staticmixer 140 could be configured as a plurality of individual static mixersarranged in series. Similarly, static mixer 130 could also be configuredas a manifold that includes a plurality of individual static mixersarranged in parallel, or as a series of individual static mixers. Itshould be understood by one skilled in the art that the presentinvention is not limited to the use of an individual static mixer forany of the elements depicted as individual static mixers in the Figures.As would be readily apparent to one skilled in the art, a plurality ofindividual static mixers arranged in series could be used, or a manifoldcontaining a plurality of individual static mixers arranged in parallelto provide a plurality of parallel flow streams could also be used.

[0115] Another embodiment of the invention is shown in FIG. 2 (system200). A first phase 210 and a second phase 220 are pumped via a pump 212and a pump 222, respectively, into a first static mixer 230 to form anemulsion. The first phase preferably comprises an active agent and apolymer, and is preferably in the form of a solution. The second phaseis preferably an aqueous solution that functions as the continuous phaseof the emulsion.

[0116] The emulsion is combined with a first portion of an extractionliquid 250, pumped via a pump 252, in a static mixer 235. Static mixer235 functions as a blending static mixer to blend the emulsion and thefirst extraction liquid. The outflow of static mixer 235 is divided intoa plurality of flow streams that flow into a manifold 240. Manifold 240includes a plurality of individual static mixers 242 configured in aparallel arrangement that provides a plurality of parallel flow streams.Although FIG. 2 shows three individual and separate static mixers 242 inmanifold 240, it should be readily apparent to one skilled in the artthat manifold 240 can be configured with more, or less, individualstatic mixers 242. In a preferred embodiment, manifold 240 includes twoindividual static mixers 242, and the outflow of static mixer 235 isdivided into two flow streams, each of the two flow streams flowingthrough one of the two individual static mixers.

[0117] The outflows of individual static mixers 242 are combined to formthe outflow of manifold 240. The outflow of manifold 240 is combinedwith a second portion of extraction liquid 250, pumped via a pump 254,in another static mixer 270. In an alternate embodiment of the presentinvention, manifold 240 is replaced with a single static mixer locatedbetween static mixer 235 and static mixer 270. In yet another alternateembodiment, manifold 240 is replaced with a plurality of individualstatic mixers arranged in series. As would be readily apparent to oneskilled in the art, static mixers 230, 235, and 270 depicted in FIG. 2as individual static mixers could be replaced with a plurality ofindividual static mixers arranged in series, or with a manifoldcontaining a plurality of individual static mixers arranged in parallel.

[0118] In one embodiment, pump 254 is configured to operate at a flowrate greater than a flow rate of pump 252. It should be understood thatthe present invention is not limited to such a flow rate configuration,and other suitable flow rates would be readily apparent to one skilledin the art.

[0119] The outflow of manifold 240 is combined with extraction liquid250 in static mixer 270, and this combining is repeated until thestarting volume of extraction liquid 250 is depleted. Once the startingvolume of extraction liquid 250 is depleted, the outflow of static mixer270 flows into a vessel 260 that is preferably initially empty, i.e.,does not contain any extraction liquid. In this manner, all ofextraction liquid 250 is introduced into the processing stream, andcombined with the emulsion in one of the static mixers.

[0120] In system 200 as shown in FIG. 2, extraction liquid 250 isintroduced into the processing stream at two different points via pumps252 and 254. In an alternate embodiment of system 200, one type ofextraction liquid could be introduced via pump 252, and a different typeof extraction liquid could be introduced via pump 254. In a furtherembodiment, second phase 220 could be used as one or both of theextraction liquids introduced via pumps 252 and 254.

[0121] Alternatively, system 200 could be modified to eliminate staticmixer 270 so that the outflow of manifold 240 flows into vessel 260 thatcontains the second portion of extraction liquid 250. System 200 couldalso be modified to add additional static mixers 270 in which additionalportions of extraction liquid 250, or other different type of extractionliquid, are combined with the flow stream.

[0122] Conclusion

[0123] While various embodiments of the present invention have beendescribed above, it should be understood that they have been presentedby way of example only, and not limitation. The present invention is notlimited to the preparation of controlled release microparticles, nor isit limited to a particular active agent, polymer or solvent, nor is thepresent invention limited to a particular scale or batch size. Thus, thebreadth and scope of the present invention should not be limited by anyof the above-described exemplary embodiments, but should be defined onlyin accordance with the following claims and their equivalents.

What is claimed is:
 1. A method of preparing microparticles, comprising:combining a first phase, comprising an active agent, a polymer, and asolvent, and a second phase in a first static mixer to form an emulsion,the emulsion forming an outflow of the first static mixer; combining theoutflow of the first static mixer and a first portion of a startingvolume of an extraction liquid for extracting solvent from the emulsionin a manifold, wherein the manifold comprises a plurality of individualstatic mixers configured to form a plurality of parallel flow streams,each of the plurality of parallel flow streams comprising at least oneof the plurality of individual static mixers; and combining an outflowof the manifold with a second portion of the extraction liquid toextract solvent from the emulsion.
 2. The method of claim 1, wherein thestep of combining the outflow of the manifold with the second portion ofthe extraction liquid comprises: allowing the outflow of the manifold toflow into a vessel containing the second portion of the extractionliquid.
 3. The method of claim 1, wherein the step of combining theoutflow of the manifold with the second portion of the extraction liquidcomprises: combining the outflow of the manifold and the second portionof the extraction liquid in a second static mixer.
 4. The method ofclaim 3, further comprising: allowing an outflow of the second staticmixer to flow into a vessel.
 5. The method of claim 1, wherein the stepof combining the outflow of the manifold with the second portion of theextraction liquid comprises: combining the outflow of the manifold andthe second portion of the extraction liquid in a second static mixer andrepeating this combining step until the starting volume of theextraction liquid is depleted.
 6. The method of claim 4, furthercomprising: continuing the step of combining the outflow of the manifoldand the second portion of the extraction liquid in the second staticmixer until the first phase is depleted; and transferring a remainder ofthe starting volume of the extraction liquid to the vessel. 7.Microparticles prepared by the method of claim
 1. 8. The microparticlesof claim 7, wherein the polymer is a poly(lactide-co-glycolide).